Gravel website http://gravelvideogame.com no longer shows the message and has returned to normal as it was before with all the information from the first Gravel.
Milestone has informed the website www.drivingitalia.net that there is no new Gravel in development or in the company's plans. It's in Italian but I have translated it with Google translate
UPDATE 15.00 - we receive from MILESTONE:
Dear editor, regarding the article published by you today 11/13, Milestone wishes to point out that at this time a sequel to Gravel is not in development or in the company's future plans. The message that appeared on the videogame website was caused by a technical problem, now resolved, about the causes we are investigating.